It's only a Sempron, running Win 2000, but only with essential services (it doesn't even have a monitor attached... just a file server and running my home automation software). I built this machine specifically for this purpose. Media Center and Homeseer are the only two services that machine provides. It has been running Windows Media Player for the library (along with Homeseer) for years before MC ever came into the picture. I keep Win 2000 on this machine for no other reason that I like to keep that machine as lean and mean as possible. It has been rock solid for the few years since I've built it.
I'm also not really sure how that would make a difference in this case, considering it's been running MC without problems for six months (including 11 before 12) -- this version is what caused this issue (and I can't see why servicing a small JPG over HTTP would take 10-30 seconds, even on an old Pentium III). I literally had been listening to music, decided to move from .198 to .226... updated both the server and clients and bam... the problem started.
Being a programmer myself, I almost think there has to be some form of an endless loop or leaky process somewhere in the code that would be new and involving cover art. It also could be very possible that this delay is just not as "noticeable" on a faster machine.
No conversion is enabled. As I said, once it gets the covert art, it flips between tracks on the client immediately (even with MC's nice fade between). In addition, the server itself is always is responsive (even with my home automation software is communicating with it) UNLESS it is serving covert art through the library server. I have various keypads around the house that can select playlists, change tracks, etc through Homeseer and MC performs the task immediately (again, so long as I don't have a client somewhere requesting cover art).
MC has to best one of the best pieces of software I have ever bought, and, thus the reason it's so important I need it working it's best. Just wanted to back up the fact that even though I'm having a few little bumps, this software rocks my world! ... literally, I suppose ;-)